US6295039B1 - Thin illuminator for reflective displays - Google Patents

Thin illuminator for reflective displays Download PDF

Info

Publication number
US6295039B1
US6295039B1 US09/139,962 US13996298A US6295039B1 US 6295039 B1 US6295039 B1 US 6295039B1 US 13996298 A US13996298 A US 13996298A US 6295039 B1 US6295039 B1 US 6295039B1
Authority
US
United States
Prior art keywords
light
reflector
linear
display
light source
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US09/139,962
Inventor
Pierre H. Mertz
Brian L. Heffner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Avago Technologies International Sales Pte Ltd
Original Assignee
Agilent Technologies Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Agilent Technologies Inc filed Critical Agilent Technologies Inc
Priority to US09/139,962 priority Critical patent/US6295039B1/en
Assigned to HEWLETT-PACKARD COMPANY reassignment HEWLETT-PACKARD COMPANY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HEFFNER, BRIAN L., MERTZ, PIERRE H.
Priority to DE69923393T priority patent/DE69923393T2/en
Priority to EP99112851A priority patent/EP0982705B1/en
Priority to JP22500999A priority patent/JP4260991B2/en
Assigned to HEWLETT-PACKARD COMPANY reassignment HEWLETT-PACKARD COMPANY CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: HEWLETT-PACKARD COMPANY
Assigned to HEWLETT-PACKARD COMPANY reassignment HEWLETT-PACKARD COMPANY MERGER (SEE DOCUMENT FOR DETAILS). Assignors: HEWLETT-PACKARD COMPANY
Assigned to AGILENT TECHNOLOGIES INC reassignment AGILENT TECHNOLOGIES INC ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HEWLETT-PACKARD COMPANY
Application granted granted Critical
Publication of US6295039B1 publication Critical patent/US6295039B1/en
Assigned to AVAGO TECHNOLOGIES GENERAL IP PTE. LTD. reassignment AVAGO TECHNOLOGIES GENERAL IP PTE. LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: AGILENT TECHNOLOGIES, INC.
Assigned to AVAGO TECHNOLOGIES ECBU IP (SINGAPORE) PTE. LTD. reassignment AVAGO TECHNOLOGIES ECBU IP (SINGAPORE) PTE. LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.
Assigned to AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD. reassignment AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD. MERGER (SEE DOCUMENT FOR DETAILS). Assignors: AVAGO TECHNOLOGIES ECBU IP (SINGAPORE) PTE. LTD.
Assigned to DEUTSCHE BANK AG NEW YORK BRANCH, AS COLLATERAL AGENT reassignment DEUTSCHE BANK AG NEW YORK BRANCH, AS COLLATERAL AGENT PATENT SECURITY AGREEMENT Assignors: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.
Assigned to AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD. reassignment AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD. TERMINATION AND RELEASE OF SECURITY INTEREST IN PATENT RIGHTS (RELEASES RF 032851-0001) Assignors: DEUTSCHE BANK AG NEW YORK BRANCH, AS COLLATERAL AGENT
Assigned to BANK OF AMERICA, N.A., AS COLLATERAL AGENT reassignment BANK OF AMERICA, N.A., AS COLLATERAL AGENT PATENT SECURITY AGREEMENT Assignors: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.
Assigned to AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD. reassignment AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD. CORRECTIVE ASSIGNMENT TO CORRECT THE NAME OF THE ASSIGNEE PREVIOUSLY RECORDED ON REEL 017207 FRAME 0020. ASSIGNOR(S) HEREBY CONFIRMS THE ASSIGNMENT. Assignors: AGILENT TECHNOLOGIES, INC.
Assigned to AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD. reassignment AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD. TERMINATION AND RELEASE OF SECURITY INTEREST IN PATENTS Assignors: BANK OF AMERICA, N.A., AS COLLATERAL AGENT
Anticipated expiration legal-status Critical
Assigned to AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITED reassignment AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.
Assigned to AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITED reassignment AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITED CORRECTIVE ASSIGNMENT TO CORRECT THE NATURE OF CONVEYANCE AND EFFECTIVE DATE PREVIOUSLY RECORDED ON REEL 047022 FRAME 0620. ASSIGNOR(S) HEREBY CONFIRMS THE MERGER. Assignors: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.
Assigned to AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITED reassignment AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITED CORRECTIVE ASSIGNMENT TO CORRECT THE EFFECTIVE DATE PREVIOUSLY RECORDED ON REEL 047185 FRAME 0643. ASSIGNOR(S) HEREBY CONFIRMS THE MERGER. Assignors: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.
Assigned to AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITED reassignment AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITED CORRECTIVE ASSIGNMENT TO CORRECT THE EFFECTIVE DATE OF MERGER PREVIOUSLY RECORDED AT REEL: 047185 FRAME: 0643. ASSIGNOR(S) HEREBY CONFIRMS THE CORRECTIVE MERGER. Assignors: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09FDISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F13/00Illuminated signs; Luminous advertising
    • G09F13/16Signs formed of or incorporating reflecting elements or surfaces, e.g. warning signs having triangular or other geometrical shape

Definitions

  • the present invention relates to display systems, and more particularly, to the illumination of display systems in which a plurality of pixels generate an image by reflecting light from one or more light sources.
  • Head-mounted computer displays may be viewed as “eye glasses” that are worn by the user to view images created by a computer or other video source. The image seen by each eye is generated on a display screen having a two dimensional array of pixels.
  • each pixel is a small mirror that is covered by a “shutter” that is controlled by the voltage of the mirror.
  • the shutter is constructed from a layer of liquid crystal on the mirrors.
  • the voltage controls the state of the liquid crystal on top of the pixel so as to modulate the reflected light.
  • a light source illuminates the pixels and the modulated reflected light from the pixels is imaged into the eye of the viewer.
  • the imaging optics typically consist of lenses that magnify the pixels and form a virtual image.
  • the light source is typically constructed from 3 LEDs that emit different colors.
  • each micro-mirror must be independent of the pixel's location in the display.
  • each pixel must appear to be an independent light source.
  • the illumination must be both spatially and angularly uniform, with the angular extent given by the acceptance angle (f-number) of the imaging optics.
  • the light source utilizes a condenser lens to collimate or slightly diverge the light to match the telecentricity of the imaging optic and an array of micro-lenses or a diffuser in the collimated light beam to provide the required diffusion. Since the light source must be outside the field of view of the user so as not to block the image generated by the display, a half silvered mirror is used to illuminate the display while allowing light reflected by the display to reach the eye of the viewer.
  • the distance between the first imaging optic and the display must be at least as great as the shortest dimension of the display to provide room for the half-silvered mirror.
  • the illuminator requires a condenser lens and diffuser which must be at least as large as the display.
  • all of the LEDs must be very close to the focal point of the collimating lens and limited in size so as to simulate a single point source and properly mix the colors of the LEDs. This constraint limits the size of the LEDs, and hence, the maximum intensity of light from the display.
  • the half-silvered mirror decreases the brightness of the display, since only one fourth of the light in the collimated beam actually reaches the viewer's eye.
  • the present invention is a display that includes an array of reflective pixels, a linear light source; and a reflector.
  • the reflector includes a cylindrical surface preferably having a parabolic cross-section, the axis of the cylindrical surface being parallel to the linear light source.
  • the linear light source is positioned relative to the reflector such that light from the linear light source is collimated by the reflector onto the array of reflective pixels.
  • the reflector is constructed from a material that is partially reflecting.
  • the linear light source preferably includes a plurality of light emitting diodes and an optical diffuser. In a color display, the light emitting diodes comprise diodes having different emission spectra.
  • the reflector is constructed from a material that reflects light of a first linear polarization while transmitting light having a linear polarization orthogonal to the first linear polarization.
  • each pixel in the array of reflective pixels preferably includes a polarization rotating cell that rotates the linear polarization vector of light reflected by the pixel in response to the receipt of an electrical signal by the pixel.
  • FIG. 1 is a cross-sectional view of a prior art display system.
  • FIG. 2 is a side view of a display system according to the present invention.
  • FIG. 3 is a top view of the display shown in FIG. 2 .
  • FIG. 4 is a cross-sectional view of a display system according to the present invention.
  • FIG. 5 illustrates the manner in which a typical prior art reflective display operates.
  • FIG. 6 is an expanded view of a reflective pixel according to the present invention illustrating the manner in which the preferred reflector material improves the efficiency of the display.
  • FIG. 1 is a cross-sectional view of the prior art display system 10 discussed above.
  • a display screen 12 is illuminated by a light source consisting of a LED 15 close to the focal point of a Fresnel lens 14 .
  • Fresnel lens 14 provides either a collimated light source or a slightly diverging light source that matches the telecentricity of the imaging optic.
  • the light leaving Fresnel lens 14 is diffused by a diffuser or micro-lens array 13 as shown at 18 .
  • the light from the source is reflected from a half-silvered mirror 16 onto display 12 .
  • the light reflected back by display 12 is imaged by lens 17 into the eye 11 of the user.
  • FIGS. 2 and 3 are side and top views of a display system 100 according to the present invention.
  • display system 100 the half-silvered mirror utilized in prior art systems is replaced by cylindrical parabolic reflector 102 .
  • FIG. 2 is a side view of display system 100 in a direction parallel to the axis of reflector 102 .
  • FIG. 3 is a top view of display system 100 .
  • Reflector 102 provides both the functions of the condenser and the partially reflecting mirror.
  • Reflector 102 is illuminated with a diffuse line source 104 , which is preferably constructed from a diffuser 105 and a plurality of LEDs 106 .
  • Display system 300 includes a display 307 , a reflector 301 , and a diffuse light source 302 .
  • the light source needs to have vertical spatial extent.
  • reflector 301 is parabolic.
  • reflector 301 is typically a hyperbolic or ellipsoidal surface. The parabolic surface converts this spatially extended source 302 to an angular cone of light having an opening angle 306 and angle 305 with respect to the display surface.
  • angle 305 is 90°.
  • the focal point 303 of reflector 301 is in the middle of source 302 .
  • the cone angle in the orthogonal direction is provided by the diffuser on the source, in a manner analogous to the micro-lenses discussed with reference to the prior art system shown in FIG. 1 .
  • the imaging optics are not telecentric, the cross-section of the cylindrical surface can be made elliptical or hyperbolic, so that the chief rays match those of the imaging optics.
  • the telecentricity in the other direction can not be matched geometrically, but the diffusion of the source in this direction provides the necessary rays.
  • the distance, D, required to accommodate reflector 102 is approximately half the distance required for the partially reflecting mirror utilized in the above-described prior art display systems.
  • the present invention has substantially less bulk and weight than prior art displays.
  • the present invention utilizes a plurality of LEDs.
  • the present invention provides substantially higher illumination of the display.
  • the light source includes a plurality of LEDs for each color of light. Typically, three different colors are utilized to construct the color image.
  • the color image is constructed by sequentially displaying the red, blue, and green images in a time-span that is shorter than the time interval in which the eye can resolve separate images.
  • the various color LEDs are positioned along the axis of the light source such that the light source is effectively three linear light sources that are superimposed on one another.
  • FIG. 5 illustrates the manner in which a typical prior art reflective display operates.
  • Pixel 200 consists of a polarization filter 201 which selects one linear polarization component of the incident light which may be viewed as consisting of two equal intensity linearly polarized components as shown at 210 .
  • polarization filter 201 selects one linear polarization component of the incident light which may be viewed as consisting of two equal intensity linearly polarized components as shown at 210 .
  • the vertical component is passed by filter 201 .
  • the light passing through filter 201 is reflected by a reflective coating 203 on the back of a liquid crystal element 202 .
  • This coating also acts as an electrode for applying a voltage across the liquid crystal element.
  • the light exiting the liquid element will have a polarization that is either vertical or horizontal depending on the potential across the liquid crystal element. If the exiting light has a polarization that has been rotated to the horizontal direction as shown at 211 , the light will be blocked by the polarization filter, and hence, the pixel will appear black. If the direction of polarization remains vertical, the light will pass through filter 201 , and the pixel will be bright.
  • the reflected light must still pass back through the half-silvered mirror 216 in prior art displays.
  • the maximum light intensity relative to the source intensity is 1 ⁇ 8 th , since one half of the light is lost in the first reflection that directs the light onto the display. Another 50% of the light intensity is lost in polarization filter 201 . Finally, yet another 50% of the remaining light is lost passing back through half silvered mirror 216 .
  • the present invention combines the polarization function of filter 201 utilized in prior art displays with the parabolic condenser lens. As a result, the effective light intensity reaching the viewer is one half of the source intensity. The manner in which this is accomplished may be more easily understood with reference to FIG. 6 which is an expanded view of a pixel according to the present invention.
  • Light from source 306 is directed toward parabolic reflector 322 .
  • the light is assumed to be unpolarized, and hence, consists of equal intensities of vertical and horizontally polarized light as shown at 310 .
  • Reflector 322 is constructed from a material that reflects light of one polarization while transmitting light of the orthogonal polarization. Such materials are known to the art.
  • 3M markets such a material under the trade name DUAL BRIGHTNESS ENHANCEMENT FILM (DBEF).
  • DBEF DUAL BRIGHTNESS ENHANCEMENT FILM
  • the vertically polarized light goes on to strike the reflective surface 203 of the pixel after passing through the liquid crystal element 202 . If the potential across the liquid crystal element is set such that the direction of polarization is rotated through 90degrees as shown at 325 , the reflected light will pass through reflector 322 and reach the eye of the viewer. In this case, the pixel will appear bright. If, however, the voltage across the liquid crystal element is such that the direction of polarization is not rotated, the light reflected by the pixel will also be reflected by reflector 322 back toward the light source 306 . In this case, the pixel will appear dark.
  • the light passing through the reflector upon reflection by the pixel does not suffer any attenuation. That is, the reflector appears transparent to that light. Accordingly, the only light loss due to reflector 322 is the initial 50 percent loss associated with the separation of the unpolarized light from source 306 into vertical and horizontal components, i.e., the loss of the light shown at 324 . Hence, the present invention has 4 times the efficiency of prior art displays.

Abstract

A display that includes an array of reflective pixels, a linear light source; and a reflector. The reflector includes a cylindrical surface, the axis of the cylindrical surface being parallel to the linear light source. The linear light source is positioned relative to the reflector such that light from the linear light source is reflected by the reflector onto the array of reflective pixels. The reflector is constructed from a material that is partially reflecting. The linear light source preferably includes a plurality of light emitting diodes and an optical diffuser. In a color display, the light emitting diodes include diodes having different emission spectra. In one embodiment of the invention, the reflector is constructed from a material that reflects light of a first linear polarization while transmitting light having a linear polarization orthogonal to the first linear polarization. In this embodiment, each pixel in the array of reflective pixels preferably includes a polarization rotating cell that rotates the linear polarization vector of light reflected by the pixel in response to the receipt of an electrical signal by the pixel.

Description

FIELD OF THE INVENTION
The present invention relates to display systems, and more particularly, to the illumination of display systems in which a plurality of pixels generate an image by reflecting light from one or more light sources.
BACKGROUND OF THE INVENTION
simplify the following discussion, the present invention will be discussed in terms of displays utilized in head mounted computer displays; however, it will be apparent to those skilled in the art from the following discussion that the present invention may be applied to other types of displays. Head-mounted computer displays may be viewed as “eye glasses” that are worn by the user to view images created by a computer or other video source. The image seen by each eye is generated on a display screen having a two dimensional array of pixels.
In one type of display, each pixel is a small mirror that is covered by a “shutter” that is controlled by the voltage of the mirror. The shutter is constructed from a layer of liquid crystal on the mirrors. The voltage controls the state of the liquid crystal on top of the pixel so as to modulate the reflected light. A light source illuminates the pixels and the modulated reflected light from the pixels is imaged into the eye of the viewer. The imaging optics typically consist of lenses that magnify the pixels and form a virtual image. The light source is typically constructed from 3 LEDs that emit different colors.
For this type of display to function properly, the intensity of light reflected by each micro-mirror must be independent of the pixel's location in the display. In addition, each pixel must appear to be an independent light source. The illumination must be both spatially and angularly uniform, with the angular extent given by the acceptance angle (f-number) of the imaging optics. In prior art systems these constraints are met by converting the three point light sources into a diffuse light beam that strikes the display at right angles to the plane of the mirrors. The light source utilizes a condenser lens to collimate or slightly diverge the light to match the telecentricity of the imaging optic and an array of micro-lenses or a diffuser in the collimated light beam to provide the required diffusion. Since the light source must be outside the field of view of the user so as not to block the image generated by the display, a half silvered mirror is used to illuminate the display while allowing light reflected by the display to reach the eye of the viewer.
This prior art solution to the illumination problem has several problems. First, the distance between the first imaging optic and the display must be at least as great as the shortest dimension of the display to provide room for the half-silvered mirror. Second, the illuminator requires a condenser lens and diffuser which must be at least as large as the display. These constraints lead to a bulky display. Both the size and the weight of this type of display are objectionable.
To collimate the light source, all of the LEDs must be very close to the focal point of the collimating lens and limited in size so as to simulate a single point source and properly mix the colors of the LEDs. This constraint limits the size of the LEDs, and hence, the maximum intensity of light from the display. In addition, the half-silvered mirror decreases the brightness of the display, since only one fourth of the light in the collimated beam actually reaches the viewer's eye.
Broadly, it is the object of the present invention to provide an improved illumination system for a reflective display.
It is a further object of the present invention to provide a display system that does not require the use of a half-silvered mirror to illuminate the pixels.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is a display that includes an array of reflective pixels, a linear light source; and a reflector. The reflector includes a cylindrical surface preferably having a parabolic cross-section, the axis of the cylindrical surface being parallel to the linear light source. The linear light source is positioned relative to the reflector such that light from the linear light source is collimated by the reflector onto the array of reflective pixels. The reflector is constructed from a material that is partially reflecting. The linear light source preferably includes a plurality of light emitting diodes and an optical diffuser. In a color display, the light emitting diodes comprise diodes having different emission spectra. In one embodiment of the invention, the reflector is constructed from a material that reflects light of a first linear polarization while transmitting light having a linear polarization orthogonal to the first linear polarization. In this embodiment, each pixel in the array of reflective pixels preferably includes a polarization rotating cell that rotates the linear polarization vector of light reflected by the pixel in response to the receipt of an electrical signal by the pixel.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a prior art display system.
FIG. 2 is a side view of a display system according to the present invention.
FIG. 3 is a top view of the display shown in FIG. 2.
FIG. 4 is a cross-sectional view of a display system according to the present invention.
FIG. 5 illustrates the manner in which a typical prior art reflective display operates.
FIG. 6 is an expanded view of a reflective pixel according to the present invention illustrating the manner in which the preferred reflector material improves the efficiency of the display.
DETAILED DESCRIPTION ON THE INVENTION
The present invention may be more easily understood with reference to FIG. 1 which is a cross-sectional view of the prior art display system 10 discussed above. A display screen 12 is illuminated by a light source consisting of a LED 15 close to the focal point of a Fresnel lens 14. Fresnel lens 14 provides either a collimated light source or a slightly diverging light source that matches the telecentricity of the imaging optic. The light leaving Fresnel lens 14 is diffused by a diffuser or micro-lens array 13 as shown at 18. The light from the source is reflected from a half-silvered mirror 16 onto display 12. The light reflected back by display 12 is imaged by lens 17 into the eye 11 of the user. It should be noted that, at most, half of the light leaving diffuser 13 reaches display 12, since mirror 16 allows half of the light to pass through the mirror. Similarly, only half of the light leaving display 12 reaches lens 17 for the same reason. It should also be noted that the minimum values for the width and height of the display system are set by the illumination optics. As noted above, such systems are bulky and have limitations on the maximum light intensity that can be delivered to the eye of the viewer.
Refer now to FIGS. 2 and 3, which are side and top views of a display system 100 according to the present invention. In display system 100, the half-silvered mirror utilized in prior art systems is replaced by cylindrical parabolic reflector 102. FIG. 2 is a side view of display system 100 in a direction parallel to the axis of reflector 102. FIG. 3 is a top view of display system 100. Reflector 102 provides both the functions of the condenser and the partially reflecting mirror. Reflector 102 is illuminated with a diffuse line source 104, which is preferably constructed from a diffuser 105 and a plurality of LEDs 106.
Refer now to FIG. 4 which is a cross-sectional view of a display system according to the present invention. Display system 300 includes a display 307, a reflector 301, and a diffuse light source 302. To provide the angular spread of the illumination required to fill the acceptance angle of the imaging optics, the light source needs to have vertical spatial extent. In the case of a telecentric system, reflector 301 is parabolic. In non-telecentric systems, reflector 301 is typically a hyperbolic or ellipsoidal surface. The parabolic surface converts this spatially extended source 302 to an angular cone of light having an opening angle 306 and angle 305 with respect to the display surface. In telecentric systems, angle 305 is 90°. The focal point 303 of reflector 301 is in the middle of source 302. The cone angle in the orthogonal direction is provided by the diffuser on the source, in a manner analogous to the micro-lenses discussed with reference to the prior art system shown in FIG. 1. If the imaging optics are not telecentric, the cross-section of the cylindrical surface can be made elliptical or hyperbolic, so that the chief rays match those of the imaging optics. The telecentricity in the other direction can not be matched geometrically, but the diffusion of the source in this direction provides the necessary rays.
It should be noted that the distance, D, required to accommodate reflector 102 is approximately half the distance required for the partially reflecting mirror utilized in the above-described prior art display systems. Hence, the present invention has substantially less bulk and weight than prior art displays. Further, the present invention utilizes a plurality of LEDs. Hence, the present invention provides substantially higher illumination of the display.
In a color display according to the present invention, the light source includes a plurality of LEDs for each color of light. Typically, three different colors are utilized to construct the color image. The color image is constructed by sequentially displaying the red, blue, and green images in a time-span that is shorter than the time interval in which the eye can resolve separate images. The various color LEDs are positioned along the axis of the light source such that the light source is effectively three linear light sources that are superimposed on one another.
As noted above, one problem with prior art displays results from the use of a partially reflecting mirror, which reduces the effective illumination by 75%. The preferred embodiment of the present invention utilizes a material for the construction of the parabolic reflector that overcomes this problem when utilized with a display that operates by rotating the polarization of the incident light. The manner in which this aspect of the present invention operates may be more easily understood with reference to FIG. 5 which illustrates the manner in which a typical prior art reflective display operates. To simplify the drawing, only one pixel of the display is shown. Pixel 200 consists of a polarization filter 201 which selects one linear polarization component of the incident light which may be viewed as consisting of two equal intensity linearly polarized components as shown at 210. In the case shown in FIG. 5, it is assumed that the vertical component is passed by filter 201. The light passing through filter 201 is reflected by a reflective coating 203 on the back of a liquid crystal element 202. This coating also acts as an electrode for applying a voltage across the liquid crystal element. The light exiting the liquid element will have a polarization that is either vertical or horizontal depending on the potential across the liquid crystal element. If the exiting light has a polarization that has been rotated to the horizontal direction as shown at 211, the light will be blocked by the polarization filter, and hence, the pixel will appear black. If the direction of polarization remains vertical, the light will pass through filter 201, and the pixel will be bright.
The reflected light must still pass back through the half-silvered mirror 216 in prior art displays. Hence, the maximum light intensity relative to the source intensity is ⅛th, since one half of the light is lost in the first reflection that directs the light onto the display. Another 50% of the light intensity is lost in polarization filter 201. Finally, yet another 50% of the remaining light is lost passing back through half silvered mirror 216.
The present invention combines the polarization function of filter 201 utilized in prior art displays with the parabolic condenser lens. As a result, the effective light intensity reaching the viewer is one half of the source intensity. The manner in which this is accomplished may be more easily understood with reference to FIG. 6 which is an expanded view of a pixel according to the present invention. Light from source 306 is directed toward parabolic reflector 322. The light is assumed to be unpolarized, and hence, consists of equal intensities of vertical and horizontally polarized light as shown at 310. Reflector 322 is constructed from a material that reflects light of one polarization while transmitting light of the orthogonal polarization. Such materials are known to the art. For example 3M markets such a material under the trade name DUAL BRIGHTNESS ENHANCEMENT FILM (DBEF). For the purposes of this discussion, it will be assumed that reflector 322 has been constructed such that vertically polarized light is reflected and horizontally polarized light is reflected. Hence, the light from source 306 that is vertically polarized is reflected toward the pixel as shown at 323 while the horizontally polarized component passes through reflector 322 as shown at 324.
The vertically polarized light goes on to strike the reflective surface 203 of the pixel after passing through the liquid crystal element 202. If the potential across the liquid crystal element is set such that the direction of polarization is rotated through 90degrees as shown at 325, the reflected light will pass through reflector 322 and reach the eye of the viewer. In this case, the pixel will appear bright. If, however, the voltage across the liquid crystal element is such that the direction of polarization is not rotated, the light reflected by the pixel will also be reflected by reflector 322 back toward the light source 306. In this case, the pixel will appear dark.
It should be noted that the light passing through the reflector upon reflection by the pixel does not suffer any attenuation. That is, the reflector appears transparent to that light. Accordingly, the only light loss due to reflector 322 is the initial 50 percent loss associated with the separation of the unpolarized light from source 306 into vertical and horizontal components, i.e., the loss of the light shown at 324. Hence, the present invention has 4 times the efficiency of prior art displays.
Various modifications to the present invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, the present invention is to be limited solely by the scope of the following claims.

Claims (6)

What is claimed is:
1. A display comprising:
an array of reflective pixels;
a linear light source comprising a line source that emits light in a pattern defined by an axis; and
a reflector comprising a cylindrical surface, the axis of said cylindrical surface being parallel to said axis of said light source, said linear light soucer being position relative to said reflector such that light from said linear light soucer is reflected by said reflector into said array of reflective pixels, said reflector comprising a material that is partially reflecting.
2. The display of claim 1, wherein said linear light source comprises a plurality of light emitting diodes and an optical diffuser.
3. The display of claim 2 wherein said light emitting diodes comprise diodes having different emission spectra.
4. The display of claim 1 wherein said reflector comprises a material that preferentially reflects light of a first linear polarization while preferentially transmitting light having a linear polarization orthogonal to said first linear polarization.
5. The display of claim 4 wherein each pixel in said array of reflective pixels comprises a polarization rotating cell that rotates the linear polarization vector of light reflected by said pixel in response to the receipt of an electrical signal by said pixel.
6. An illumination system for illuminating a reflective display, said illumination system comprising:
a linear light source comprising a line source that emits light in a pattern defined by an axis; and
a reflector comprising a cylindrical surface, the axis of said cylindrical surface being parallel to said axis of said linear light source, said linear light source being positioned relative to said reflector such that light from said linear light source is reflected by said reflector onto said reflective display, said reflector comprising a material that preferentially reflects light of a first linear polarization while preferentially transmitting light having a linear polarization orthogonal to said first linear polarization.
US09/139,962 1998-08-25 1998-08-25 Thin illuminator for reflective displays Expired - Lifetime US6295039B1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US09/139,962 US6295039B1 (en) 1998-08-25 1998-08-25 Thin illuminator for reflective displays
DE69923393T DE69923393T2 (en) 1998-08-25 1999-07-02 Thin illumination device for reflective display devices
EP99112851A EP0982705B1 (en) 1998-08-25 1999-07-02 Thin illuminator for reflective displays
JP22500999A JP4260991B2 (en) 1998-08-25 1999-08-09 Display device

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US09/139,962 US6295039B1 (en) 1998-08-25 1998-08-25 Thin illuminator for reflective displays

Publications (1)

Publication Number Publication Date
US6295039B1 true US6295039B1 (en) 2001-09-25

Family

ID=22489108

Family Applications (1)

Application Number Title Priority Date Filing Date
US09/139,962 Expired - Lifetime US6295039B1 (en) 1998-08-25 1998-08-25 Thin illuminator for reflective displays

Country Status (4)

Country Link
US (1) US6295039B1 (en)
EP (1) EP0982705B1 (en)
JP (1) JP4260991B2 (en)
DE (1) DE69923393T2 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050122291A1 (en) * 2003-12-04 2005-06-09 May Gregory J. Optically addressable pixel and receptacle array

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6785049B1 (en) 2000-01-31 2004-08-31 3M Innovative Properties Company Illumination system for reflective displays
US7301587B2 (en) * 2003-02-28 2007-11-27 Nec Corporation Image display device and portable terminal device using the same

Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4088400A (en) * 1972-12-29 1978-05-09 Thomson-Csf Display devices
JPH06110033A (en) 1992-09-28 1994-04-22 Mitsubishi Electric Corp Liquid crystal display device
US5467206A (en) * 1993-07-09 1995-11-14 Thomson-Csf Color display device with intervening lens and spatial filter or with overlapping beams of chromatically separated light between the chromatic separator and lens array
US5467205A (en) 1993-04-28 1995-11-14 Olympus Optical Co., Ltd. Image display system with right and left eye illuminating means
US5506705A (en) 1993-09-01 1996-04-09 Sharp Kabushiki Kaisha Goggle type display apparatus
US5673059A (en) * 1994-03-23 1997-09-30 Kopin Corporation Head-mounted display apparatus with color sequential illumination
US5684354A (en) 1993-10-05 1997-11-04 Tir Technologies, Inc. Backlighting apparatus for uniformly illuminating a display panel
US5757341A (en) * 1994-10-14 1998-05-26 U. S. Philips Corporation Color liquid crystal projection display systems
US5812225A (en) * 1995-07-25 1998-09-22 Sextant Avionique Liquid crystal display screen
US5853240A (en) * 1995-12-22 1998-12-29 Sharp Kabushiki Kaisha Projector using a small-size optical system
US5980054A (en) * 1996-05-09 1999-11-09 Matsushita Electric Industrial Co., Ltd. Panel-form illuminating system

Patent Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4088400A (en) * 1972-12-29 1978-05-09 Thomson-Csf Display devices
JPH06110033A (en) 1992-09-28 1994-04-22 Mitsubishi Electric Corp Liquid crystal display device
US5467205A (en) 1993-04-28 1995-11-14 Olympus Optical Co., Ltd. Image display system with right and left eye illuminating means
US5467206A (en) * 1993-07-09 1995-11-14 Thomson-Csf Color display device with intervening lens and spatial filter or with overlapping beams of chromatically separated light between the chromatic separator and lens array
US5506705A (en) 1993-09-01 1996-04-09 Sharp Kabushiki Kaisha Goggle type display apparatus
US5684354A (en) 1993-10-05 1997-11-04 Tir Technologies, Inc. Backlighting apparatus for uniformly illuminating a display panel
US5673059A (en) * 1994-03-23 1997-09-30 Kopin Corporation Head-mounted display apparatus with color sequential illumination
US5757341A (en) * 1994-10-14 1998-05-26 U. S. Philips Corporation Color liquid crystal projection display systems
US5812225A (en) * 1995-07-25 1998-09-22 Sextant Avionique Liquid crystal display screen
US5853240A (en) * 1995-12-22 1998-12-29 Sharp Kabushiki Kaisha Projector using a small-size optical system
US5980054A (en) * 1996-05-09 1999-11-09 Matsushita Electric Industrial Co., Ltd. Panel-form illuminating system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050122291A1 (en) * 2003-12-04 2005-06-09 May Gregory J. Optically addressable pixel and receptacle array

Also Published As

Publication number Publication date
DE69923393D1 (en) 2005-03-03
DE69923393T2 (en) 2005-12-22
JP4260991B2 (en) 2009-04-30
EP0982705B1 (en) 2005-01-26
JP2000098918A (en) 2000-04-07
EP0982705A3 (en) 2000-10-11
EP0982705A2 (en) 2000-03-01

Similar Documents

Publication Publication Date Title
KR100386725B1 (en) Optical System for Head Mount Display
US6488389B2 (en) Image generator having an improved illumination system
US7841726B2 (en) Illumination system and projection system incorporating the same
US7234820B2 (en) Illuminators using reflective optics with recycling and color mixing
KR100388819B1 (en) Optical System for Head Mount Display
KR100864139B1 (en) Method and apparatus for displaying 3d images
US5796526A (en) Illumination optics for spatial light modulator
US6490104B1 (en) Illumination system for a micro display
US6160667A (en) Apparatus and method for creating and displaying planar virtual images
US6944375B2 (en) Optical element and illuminator and projection display device
US5268775A (en) Contrast enhancement and ghost elimination, for reflective light valve system
US6364487B1 (en) Solid state based illumination source for a projection display
US5626410A (en) Rear projection screen with uniform brightness for tiling the images from an array of projectors
US6796655B2 (en) Projection-type display apparatus
US6824275B2 (en) Folded projection lens
JP2001516472A (en) Multi-color band scroll with single panel light valve
CA2710963A1 (en) Light multiplexer and recycler, and micro-projector incorporating the same
US5995071A (en) Reflective display utilizing fresnel micro-reflectors
US6784946B1 (en) Assembly, in which light from a light source is directed onto a surface
JP2004505290A (en) Black serrated optical panel
JP3870191B2 (en) Apparatus for projecting a multicolor image onto a projection screen
US6295039B1 (en) Thin illuminator for reflective displays
US20100103380A1 (en) Critical abbe illumination configuration
JPH0588145A (en) Projection optical device
KR100354149B1 (en) Optical System for Head Mount Display

Legal Events

Date Code Title Description
AS Assignment

Owner name: HEWLETT-PACKARD COMPANY, CALIFORNIA

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MERTZ, PIERRE H.;HEFFNER, BRIAN L.;REEL/FRAME:009503/0192

Effective date: 19980825

AS Assignment

Owner name: HEWLETT-PACKARD COMPANY, COLORADO

Free format text: CHANGE OF NAME;ASSIGNOR:HEWLETT-PACKARD COMPANY;REEL/FRAME:010648/0518

Effective date: 19980520

AS Assignment

Owner name: HEWLETT-PACKARD COMPANY, COLORADO

Free format text: MERGER;ASSIGNOR:HEWLETT-PACKARD COMPANY;REEL/FRAME:010759/0049

Effective date: 19980520

AS Assignment

Owner name: AGILENT TECHNOLOGIES INC, CALIFORNIA

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:HEWLETT-PACKARD COMPANY;REEL/FRAME:010977/0540

Effective date: 19991101

STCF Information on status: patent grant

Free format text: PATENTED CASE

FEPP Fee payment procedure

Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

FPAY Fee payment

Year of fee payment: 4

AS Assignment

Owner name: AVAGO TECHNOLOGIES GENERAL IP PTE. LTD., SINGAPORE

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:AGILENT TECHNOLOGIES, INC.;REEL/FRAME:017207/0020

Effective date: 20051201

AS Assignment

Owner name: AVAGO TECHNOLOGIES ECBU IP (SINGAPORE) PTE. LTD.,S

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:017675/0518

Effective date: 20060127

Owner name: AVAGO TECHNOLOGIES ECBU IP (SINGAPORE) PTE. LTD.,

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:017675/0518

Effective date: 20060127

FPAY Fee payment

Year of fee payment: 8

FPAY Fee payment

Year of fee payment: 12

AS Assignment

Owner name: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD

Free format text: MERGER;ASSIGNOR:AVAGO TECHNOLOGIES ECBU IP (SINGAPORE) PTE. LTD.;REEL/FRAME:030369/0528

Effective date: 20121030

AS Assignment

Owner name: DEUTSCHE BANK AG NEW YORK BRANCH, AS COLLATERAL AGENT, NEW YORK

Free format text: PATENT SECURITY AGREEMENT;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:032851/0001

Effective date: 20140506

Owner name: DEUTSCHE BANK AG NEW YORK BRANCH, AS COLLATERAL AG

Free format text: PATENT SECURITY AGREEMENT;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:032851/0001

Effective date: 20140506

AS Assignment

Owner name: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD., SINGAPORE

Free format text: TERMINATION AND RELEASE OF SECURITY INTEREST IN PATENT RIGHTS (RELEASES RF 032851-0001);ASSIGNOR:DEUTSCHE BANK AG NEW YORK BRANCH, AS COLLATERAL AGENT;REEL/FRAME:037689/0001

Effective date: 20160201

Owner name: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD

Free format text: TERMINATION AND RELEASE OF SECURITY INTEREST IN PATENT RIGHTS (RELEASES RF 032851-0001);ASSIGNOR:DEUTSCHE BANK AG NEW YORK BRANCH, AS COLLATERAL AGENT;REEL/FRAME:037689/0001

Effective date: 20160201

AS Assignment

Owner name: BANK OF AMERICA, N.A., AS COLLATERAL AGENT, NORTH CAROLINA

Free format text: PATENT SECURITY AGREEMENT;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:037808/0001

Effective date: 20160201

Owner name: BANK OF AMERICA, N.A., AS COLLATERAL AGENT, NORTH

Free format text: PATENT SECURITY AGREEMENT;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:037808/0001

Effective date: 20160201

AS Assignment

Owner name: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD

Free format text: CORRECTIVE ASSIGNMENT TO CORRECT THE NAME OF THE ASSIGNEE PREVIOUSLY RECORDED ON REEL 017207 FRAME 0020. ASSIGNOR(S) HEREBY CONFIRMS THE ASSIGNMENT;ASSIGNOR:AGILENT TECHNOLOGIES, INC.;REEL/FRAME:038633/0001

Effective date: 20051201

AS Assignment

Owner name: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD., SINGAPORE

Free format text: TERMINATION AND RELEASE OF SECURITY INTEREST IN PATENTS;ASSIGNOR:BANK OF AMERICA, N.A., AS COLLATERAL AGENT;REEL/FRAME:041710/0001

Effective date: 20170119

Owner name: AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD

Free format text: TERMINATION AND RELEASE OF SECURITY INTEREST IN PATENTS;ASSIGNOR:BANK OF AMERICA, N.A., AS COLLATERAL AGENT;REEL/FRAME:041710/0001

Effective date: 20170119

AS Assignment

Owner name: AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITE

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:047022/0620

Effective date: 20180509

AS Assignment

Owner name: AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITE

Free format text: CORRECTIVE ASSIGNMENT TO CORRECT THE NATURE OF CONVEYANCE AND EFFECTIVE DATE PREVIOUSLY RECORDED ON REEL 047022 FRAME 0620. ASSIGNOR(S) HEREBY CONFIRMS THE MERGER;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:047185/0643

Effective date: 20180509

AS Assignment

Owner name: AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITE

Free format text: CORRECTIVE ASSIGNMENT TO CORRECT THE EFFECTIVE DATE PREVIOUSLY RECORDED ON REEL 047185 FRAME 0643. ASSIGNOR(S) HEREBY CONFIRMS THE MERGER;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:047476/0845

Effective date: 20180905

AS Assignment

Owner name: AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE. LIMITE

Free format text: CORRECTIVE ASSIGNMENT TO CORRECT THE EFFECTIVE DATE OF MERGER PREVIOUSLY RECORDED AT REEL: 047185 FRAME: 0643. ASSIGNOR(S) HEREBY CONFIRMS THE CORRECTIVE MERGER;ASSIGNOR:AVAGO TECHNOLOGIES GENERAL IP (SINGAPORE) PTE. LTD.;REEL/FRAME:047959/0296

Effective date: 20180905